Method for etching metals



March 25, 1958 w. P. LANGSFELD 2,828,192

METHOD FOR ETCHING METALS Filed Oct. 4, 1954 I 2 Sheets-Sheet 1INVENTOR.

N SFELD 7 March 25, 1958 w. P. LANGSFELD 2,828,192

METHOD FOR ETCH'ING METALS 2 Sheets-Sheet 2 Filed Oct. 4, 1954'INVENTOR.

w w a. U H

Il /mm I? Lmvasrao flTTORNEY- United States Pa ent 2,828,192 METHOD nonETCHING METALS William P. Langsfeld, Huntington Park, Califi, assignorto Turco Products, Inc., Los Angeles,'Cahf'., a corporation ofCalifornia Application October 4, 1954, Serial o.460,o12

2 Claims. 01. 41-42 1 This invention relates to improvements in.thechemical etching of metals, and is more particularly concerned withnovel procedure and apparatus for the control of foam formed on thesurface of the etching bath.

It is known to etch acid soluble metals, such as magnesium, zinc, iron,titanium,'nickel and their alloys with an acid solution such as aqueousnitric acid. It is also known to etch alkali soluble metals such asaluminum and its alloys with a solution having a solvent action on thealuminum or alloy surface, such as a hot aqueous alkali solution, forexample, one containing sodium hydroxide. I

One common method of carrying out the etching operation is to immersethe metal partto be etched in an etching bath contained in a tank.However, during the' etching reaction, hydrogen gas is liberated, andthis gas, together with entrained water vapor including dropletscontaining etchant, generally produces a layer of froth or foam on thesurface of the etching solution. When the part or work piece beingetched is removed from the bath, the froth causes a wavy etch pattern tobe superimposed on the etch of the part due to passage thereof throughthis froth layer. Also, the etchant contained in the entrained vaporsabove the bath tends to coat and pre-etch the metal part prior tovandduring immersion thereof, thereby resulting in a non-uniform final etchpattern. Also, when the part is only partially immersed during theetching period, non-uniform etching takes place in the area of contactof the froth with the exposed surfaces of the work piece.

One object of the invention is to provide novel apparatus and procedurefor efficiently etching a metal part.

Another object is the provision of procedure and apparatus for etching ametal part while eliminating or minimizing undesired additional etchingcaused by stationary contact of the part with the surface froth, or bypassage of the part through the surface froth during immersion orremoval of the part from the etching solution.

Yet another object is to provide novelapparatus and procedure forcontrolling the surface froth in an etching bath.

Still another object of the invention is to substantially remove suchsurface froth from around a part to be etched during immersion thereofin or withdrawal thereof from the bath following the etching operation.

Still another object is to minimize the proportion of en-' trainedetching agent in the vapors in the zone above the etching bath.

A still further object is to cool the zone above the etching bath.

Another aim of the invention is to achieve the foregoing objectsemploying an alkali solution as the'etching agent fortreatment of analuminum or aluminum alloy part, that is, one composed of aluminum'..asthe base metal.

Other objects and advantages willapp'ear from the following descriptionof my invention:

I'have' found that the adverse" effects of 'such'froth or ice immersedin such solution during the etching period, can

be substantially eliminated or to a great extent alleviated by directinga stream. of air or an air blast, preferably containing moisture, at theliquid etching bath surface below the froth line and against the part.Preferably, means in the form of a fan shaped spray nozzle is employedto emit a stream of spray which acts like a knife to sweep away thefroth'and to strip adherent etchant from the surface of the part. Theair stream destroys the froth around, or in the immediate vicinity of,the part by breaking up the bubbles of foam. The nozzle is preferablypositioned a short distance above the surface of the froth and ismounted so that it is inclined downwardly at an acute angle to theliquid surface. In this manner, impingement of the air stream or blastthrough the froth and against. the metal part while it is partiallysubmerged in the bath during etching, or while such part is passingthrough the froth, pushes the froth back and restrains it from makingcontact with the part.

The moisture to air ratio in the moist air stream preferably employedmay be adjusted to include the desired amount of moisture in the airblast. For example, the amount of water in the air stream may be smallin comparison to the loss of water in .the system by evaporation andchemical reaction in such etching process, wherein water is consumed inthe reaction, as in the case for example in etching aluminum withcaustic soda. Preferably, the amount of water in the air stream isadjusted to add approximately the water necessary to maintain' solutionlevel as well as the concentration of the etching bath. The presence ofwater in the air blast tends to prevent any undesired etching in theexposed portionsof the work piece above the bath surface, or anyfurther.

I rise of vapors containing entrained etching agent through such blanketand into the space above the tank. This greatly reduces the extent ofundesirable pre-etching which takes place due to coating of the metalsurface of the work piece with such entrained etchant while the workpiece extends into or is passing through the zone above the bath priorto and during immersion thereof in the bath. It also aids in preventingformation of a coat of etchant solution on the work piece whilebeingwithdrawn from the bath. Reduction of the amount of entrained etchantsolution above the bath also materially decreases corrosion of overheadtank equipment. Also, by using additional air streams, preferably moistair, the froth orfoam can be controlled over the entire tank surface,and the air stream or streams impinging in a partially lateral directionon the froth layer, direct or sweep the liberated hydrogen gas andentrained etchant vapors to the exhaust outlets at the sides of thetank.

Below is described a novel apparatus for carrying out the inventionprocedure, taken in connection with the accompanying drawings, wherein:

Fig. l is a cross section in elevation of the invention device; 7 i iFig. 2 is a plan view of the device of Fig. 1;

Fig. 3 is a fragmentary section in elevation taken on line 3--3 of Fig.2; j v V j Fig. 4 is essentially an enlarged fragmentary sectionPatented Mar. 25, 1958 evi Fatal? 0. e re en s a. k, n. ehlme e i orkstes Parts on. he ts. are tehe 'qr; il i e dtq 1 nt atiqn f; DdYQ 9 1mmi imhin a ned nt et ank. he e: he: W rk n e e ar c mposed. an. acid:oluble. met 19!! as, itanium. t mrmer. sta nle s el m n si m z ne ttheill y e o'l' nt o ut on. hnt e of suiWlEFFiQfiQMPQSifiQI hjeha queeuhitrie, queous hydrofluq e.as de.antlmi V n yq lth j reot lte tal ses/sst l i. h m ntion e. etehina r. V .7 r r ana utnih enabminum al eyvmateria s, lkali o uhlet l ot j que ust slut pn is. mnleyede hte hins anta kal l uehasl o u n Qrpetas: un, hyd ex e -s dium nh phat g em sh. ie, ke o m xtu s, he eon Pie. ra lya a qd utu ydrex: i e so on s se .vThe alkali on ent a nsemployed n. h e, e chin seludonsm w, an e r m 0.1,o 10 normal. Temperature of, thesolutionlin' the etchingtanlg isgenerally maintainedin a rangesayfrom 100 degrees F. b .ut. boilingding, re m n o e e lower temperaturesmay, also be. used. Numeral, 11represents a layer of frothor foam which forms, on thesurface of the.

liguid intank 10 frornjheetching reaction as previously, pointed out.

Tank, 1Q has I a, hollow. flange, 12 ;disp0sed, aboutthe.

n i e p rip ry. f h nk uf ihe l l ange ormi a trough for. thefrothcrfoam. A short.cionduit-130,, communicateswith hq trough12,,theother, end of,co nv edges. of; the oppositesides 16,and 17 of.tank 1 0i is apaiif. of tracks, or guide channels 18,

A. number of manifolds 22, shown as,,four in Fig. 1,

are suspended in the, upper, portion of, tank 10. The

manifolds 22 are elongated hllowmemberswhich extendalmost.acrossthe-entirewidth of the tanlc, each of suchmanifolds, havingendwalls 21 and inclined side portions.2 3 .whi ch slope downward andinwardly, at equal anglestolhevertical, as seen in'Fig. 4. The washed,

botto n 25 .of. the manifolds, are, parallel to .each other.

Positioned on the. outer surface. ofeachof the. sloping sides 23 .ofthe.manifoldsisa nozzle 30, preferablyhaving afan shapedcrosssection, withforwardly tapering sides 29,v The, nozzles 30.,areofawidthsubstantially. coextensive with thelengthofthe manifolds 22,asseenin Fig. 2,-

and are secured by suitable means such; as. bolts (notshoyvn) to sides23 ,of the manifolds, with the longitudinal axis of the nozzlesparallel'to the longitudinal axis of the manifolds. Nozzles 30 each have a,squareintegrallug 26 centrally positioned along, the .rear wall 36 thereof,

which lug.,fits into a square aperture;.26.f in the center. of

the,. sloping sides 23 of the manifold, each lug 2 6 having a centralaperture 27 .thereinwhichis in alignmentwith an aperturefiljn the, ,rearwall 36 0f the nozzle. charge orificelor slot,32 is centrally positionedin the,

forward. end 37 of thenozzlesii), opposite, apertures 27 and 3 1. It isseenthat the nozzles 30,, that is along.th e transverse. X,--X,axis,.thereof, are inclined at an angle to the, horizontal, axis of; tank,1tt,,and that such, nozzles are approximately on a level ,with trougl rlz for a, .reason pointed hu X e e Eae z t hemh teld hasa n inletduction of i nder.pgtess reintes he-man tel s yn fiap peii.

Manifolds 22 e eeh uspende ve he. d t: ehi .1s,: u du es erwt legen -1gto the with the nozzles 30 positioned thereon 34 centrally connected tothe top 24 thereof for intro.

in the tank by means of a pair of double hooked arms 38; the lower hooks42*of'which are receiveddn ringbolts 39 which are threadedly received inthe top of the manifolds. The upper hooks 43 of the arms 38 are loopedover a shaft 39 to be supported thereon. A pair of wheels 40 aresuitably mounted at the opposite ends of each of shafts 39, saidwheels}, being disposed in the pp hannels racks. 8,. for. euid ..d mo mt therein along the top of tank 102 It is thus-seen-that the manifoldsnd heir: ssoeiates in ttsa nelurli g nozzles; 3t);- carrheovedttghanyt-desi-redpositionnaerosss hetank between the end walls 41thereof. 7

The w tlttni ees.enme al pa t Aiton xamdejn the form ofaluniinum oraluminum alloy plates, are suspended from suitable-clamptmemhersnlfissupported from rings 48 on ropes or chains 47 in turn controlled bya hoisting mechanism such as a crane, not shown. The maniteld. ssemh iesre. mo ed to e red position fore am 1e, as shoyvn imfiigsd and "2,andth'e metal plates. .4,S,,to beetchjedjareimmersedjvertically in ,thesolt1 tion adjacent the, manifold assemblies; Figs; 1 and" 2 show threeplate s 451 with again of manifold'asse nblies disposedbetvi eencach;ofj e thr eejp lates. It is obvious, of course, that' the numlpjerof'workpieces' 45f'andthe numherqfman told; Pr v d d hat tj e st. one. jier ozz es 3018 d e wa d.. a hm t lih rfae ndergp nstet h s, the tank.

n t er- Q. mmerse, heworlqpiec s. pl s 45? inv the etching bath'll', orto remove them from theb'ath} a tream. Q pr ab y; moi t. air tom lmanifolds: 22.. s."

ejected frornihe orifice 3 2 ofgnpzzles w against the, sur; face Q othetp a es, 5.-.

tsnotednhatdhe n .zz e itl)' e.v loe edi a ove,

he urface. 1. a: .th t re h, ,lhyen 1.1,, uch vsu f ace.. .eii;1g,.

i i 591120 4 nez less is desi ned: eemitt re l-y' hi hly, i e s am,52.-. fr, o ha re sgat elat els, arser r a of pin ement ofttheair:

r arna sa nst the; iaeentt urfae fitl fith plat s 5- Also it is; notedthatfiht rigts or streams: of preferably; moisttair are directeddownward at-such anflangle; as to,

sweep the froth back away frQmJhesurfaces, 5i) ofthe P tes, extendin hroh: h i reth ay r; 1,,, il t he plates; are ,statiena yr hertei t rt reiin l w r d t t t dr o htthelfreth ayer, .senthat t-t i rt thiissubstantia y prevented r frornrthus. ontcting; heepl test 5:- h is:targeaerifiee; 32;; be; e igned: o ave: a; iz nd. ap epe ntlonr e; esirdw leei y f: r r .-v

In -this manner; surfa s; 6;: ofivp a es; 55 eingm: mersed iruthe;solutionfor etchingmre stripped ofmny entrainedsetchanhdepositednnthet-surfaees thereof especiallysduring :passage through -;the2011.6:53, above the. etch: ing solution in the tank. nificance; wherethe: plates 45 {are being; withdrawn from the etching solution'following treatment therein, surfaces; 50 0f Iplates- 45 arestripped-and irinsed of adhering etch: ant by the blasts; of; preferablymoist air whichwash: down the platesurfacem-Sfla Also, as to; anyetchantunrinsedfromlthe surfacessoflthe plates 5ft y-the moist; air blasts, thelatter will provide the metal surfaces with; a protectivecoating-whichwill imaterially reduce or halt the action of any residual adheringetchant and prevent. attack by a ny cartrained caustic-etchant in the:vapors abovethe" bathi The ratio ofmoisture in the air streams can; be-varied to produce certain efiects. Thus, for example, sufficient terlmay, e. pr nt he. a r. streams, to esult. n

Washing down of the urtacesnfith s rhpi eel tend: 1

ssernblies rnay be varied as desireds lo atecuat b ntn -level bi umen-12., T e eharees Further, and of particular Sigt tion of any adheringetching agent. This washing phenomenon can be accentuated by stillfurther increasing the amount of moisture in the air streams so long asany undesired dilution of the etching bath is not obtained. If desired,such washing action can be reduced by decreasing the amount of moisturein the air streams and relying on the sweeping effect of the air streamsto give the protection against the foam action previously dis cussed.However, it is preferable to have sufficient water in the air streams togive a washing effect and to compensate for water lost in the etchingbath.

While the application of the invention has been described above chieflywith respect to passage of a work piece through the froth layer duringits immersion into or Withdrawal from the solution, the streams of moistair can be directed against the part while the latter is maintainedstationary in the bath during etching, where only a portion of the partis immersed. Under these circumstances the streams of air keep the frothsubstantially free from contact with the exposed surfaces of the partextending through the layer, as in the case where the part is movingthrough such layer during immersion in or removal of the part from theetching solution.

Also, the relatively cool streams of air emitted from the nozzles 30have a lateral pressure component and form a sort of blanket of cool airabove the froth layer in tank 10. Since the warm vapors containingentrained etchant and the hydrogen gas evolved in the etching reactionrise from the solution at about atmospheric pressure, such vapors andhydrogen gas are essentially prevented from rising through the streamsof air emitted from the nozzles and acting as a blanket, and are sweptlaterally toward the sides of the tank beneath the air streams from thenozzles, and into suitable outlets such as conduit 13 and the stack 14.This materially cuts down the amount of entrained etchant in the zoneabove the bath and thus reduces pre-etching of a metal part passingthrough this zone into the solution, and prevents formation of aresidual coat of etchant on the part during removal thereof followingetching.

As previously noted, the ratio of water to air in the moist air streamsdirected against plates 45 may be adjusted to approximately balance theamount of water lost in tank 10. If, however, smaller ratios of waterare employed in the air stream or blast, additional water may be addedto the tank, as desired, through pipe 55 connected by bracket 56 to thetop of the tank. Vapors and hydrogen gas liberated in the reaction andpassing with any overflowing froth into pipe 13 and stack 14 are ventedtherein, and froth dropping into the bottom of the stack is drainedtherefrom through line 15.

The instant invention is applicable to the etching of any suitablemetals including, in addition to aluminum, iron, nickel, magnesium,zinc, titanium stainless steel, etc., and their alloys. Further, it isnoted that aluminum and its alloys may be etched in acid solutions suchas hydrochloric acid or salts as for example ferric sulfate, as well asalkali solutions.

The following advantages are obtainable according to the invention: (1)control of foam and froth, (2) uniform etching of a metal part in anetching bath containing a froth layer on the surface thereof, (3)directing of the hydrogen gas and entrained etchant fumes to the exhaustequipment, (4) reduction of the amount of entrained etchant, forexample, caustic alkali, in the vapors above the etching bath, (5)prevention or reduction of attack by any such entrained etchant on themetal part as aluminum or an alloy thereof, being treated, particularlyby washing down of the part by the air streams, (6) cooling of the metalpart by the air streams to reduce or stop the action of any etchantunrinsed from the surface of the metal part, (7) cooling of the zoneabove the bath, and (8) protecting the overhead equipment from thecorrosive action of vapors containing entrained etchant.

Of course, it will be understood that the apparatus described hereinshould be constructed of materials which are substantially inert toattack by the etchant solutions employed, and those skilled in this artwill know how to select such materials.

While I have described a particular embodiment of my invention for thepurpose of illustration, it should be understood that variousmodifications and adaptations thereof may be made within the spirit ofthe invention as set forth in the appended claims.

I claim:

1. The process of etching a metal work piece in an etching solutioncontaining a layer of froth on the surface thereof, which comprisespassing said work piece through said layer into said solution, etchingsaid work piece in said solution, passing said work piece out of saidsolution and through said froth layer, and directing a moist air streamfrom a point above the surface of the froth into said froth at an acuteangle to the surface of said solution below the froth line and againstsaid work piece during passage thereof through said froth layer bothinto and out of said solution.

2. The process of etching a metal work piece in an etching solutioncontaining a layer of froth on the surface thereof, which comprisespassing said work piece through said layer into said solution, etchingsaid work piece in said solution, passing said Work piece out of saidsolution and through said froth layer, and directing a moist air streamfrom a point above the surface of the froth, into said froth at an acuteangle to the surface of said solution below the froth line and againstsaid work piece during passage thereof through said froth layer out ofsaid solution.

I References Cited in the file of this patent UNITED STATES PATENTS1,081,289 Albert Dec. 16, 1913 2,293,201 Gaebel Aug. 18, 1942 2,347,511Scarzello et a1 Apr. 25, 1944 2,370,495 Sebell Feb. 27, '1945 2,390,007Sherman Nov. 27, 1945 2,566,142 Powers Aug. 28, 1951 2,724,918 TrimanNov. 29, 1955

1. THE PROCESS OF ETCHING A METAL WORK PIECE IN AN ETCHING SOLUTIONCONTAINING A LAYER OF FORTH ON THE SURFACE THEREOF, WHICH COMPRISESPASSING SAID WORK PIECE THROUGH SAID LAYER INTO SAID SOLUTION, ETCHINGSAID WORK PIECE IN SAID SOLUTION, PASSING SAID WORK PIECE OUT OF SAIDSOLUTION AND THROUGH SAID FORTH LAYER, AND DIRECTING A MOIST AIR STREAMFROM A POINT ABOVE THE SURFACE OF THE FROTH INTO SAID FROTH AT AN ACUTEANGLE TO THE SURFACE OF SAID SOLUTION BELOW THE FROTH LINE AND AGAINSTSAID WORK PIECE DURING PASSAGE THEREOF THROUGH SAID FROTH LAYER BOTHINTO AND OUT OF SAID SOLUTION.